Yum install XXX reports an error

yum install xxx

Loaded plugins: fastestmirror
Repository base is listed more than once in the configuration
Repository updates is listed more than once in the configuration
Repository extras is listed more than once in the configuration
Repository centosplus is listed more than once in the configuration
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#6 - “Could not resolve host: mirrorlist.centos.org; Temporary failure in name resolution”

One of the configured repositories failed (Unknown),
and yum doesn’t have enough cached data to continue. At this point the only
safe thing yum can do is fail. There are a few ways to work “fix” this:

 1. Contact the upstream for the repository and get them to fix the problem.


 2. Reconfigure the baseurl/etc. for the repository, to point to a working
    upstream. This is most often useful if you are using a newer
    distribution release than is supported by the repository (and the
    packages for the previous distribution release still work).


 3. Disable the repository, so yum won't use it by default. Yum will then
    just ignore the repository until you permanently enable it again or use
    --enablerepo for temporary usage:


        yum-config-manager --disable <repoid>


 4. Configure the failing repository to be skipped, if it is unavailable.
    Note that yum will try to contact the repo. when it runs most commands,
    so will have to try and fail each time (and thus. yum will be be much
    slower). If it is a very temporary problem though, this is often a nice
    compromise:


        yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64

dns The problem of resolution , Treatment method ：
vim /etc/resolv.conf Join in ：

nameserver 8.8.8.8 The server IP
nameserver 8.8.4.4 gateway
search localdomain